1. Field of the Invention
This invention is directed to an apparatus and method for generating a vacuum source that is sufficient to operate vacuum-controlled brakes of a trailer towed by a vehicle and controlling a vacuum pump for efficient generation of the vacuum source.
2. Description of Related Art
The disclosure of U.S. Pat. No. 5,823,637 provides background relevant to the present invention and is herein incorporated by reference.
Towed trailers are commonly used on roadways to haul various loads from one place to another. Trailers provide cargo capacity to vehicles designed primarily to tow, such as large diesel trucks, and supplement the cargo capacity of other vehicles, such as passenger cars, vans, pickup trucks, dual rear axle trucks, sport utility vehicles, and other types of vehicles capable of towing a trailer. Because different types of trailers can be towed, the type of added cargo carrying capacity is flexible depending on the trailer type. For example, a diesel cab can alternately carry a load of retail electronics in an enclosed freight trailer or gasoline in a tank trailer, while a pickup truck can pull a fishing boat or transport horses using the appropriate trailers.
Unfortunately, in many cases, while the tow vehicle may be powerful enough to pull a given trailer, the tow vehicle may not have adequate braking capability to slow the vehicle and the trailer at a safe rate. Accidents can result due to insufficient braking capability in the tow vehicle to stop the combined vehicle and trailer in time to prevent an accident. In cases where the tow vehicle has adequate braking capacity to slow the combined mass of the tow vehicle and the trailer, towing a trailer can still be hazardous. As the tow vehicle's brakes are applied, the tow vehicle slows, and the braking force of the tow vehicle's brakes is transferred to the trailer through a pivoted coupling between the tow vehicle and the trailer. This will normally slow the trailer along with the tow vehicle under ideal braking conditions. If, however, braking occurs during a turn, for example, or in a rapid manner, such as in a panic stop, or in other less than ideal conditions, the tow vehicle could slow while the trailer's momentum continues to carry the trailer into the tow vehicle. This can cause the trailer to swing to one side of the tow vehicle, pivoting about its coupling to the tow vehicle. This condition is commonly referred to as a “jackknife.” Jackknifing has been the cause of many serious, often fatal, road accidents.
Safely towing a trailer with a vehicle often requires an independent brake system for the trailer. For effective operation, the trailer brake system should be coupled to the tow vehicle brake system in a manner that coordinates the braking action of the two systems when the driver applies the tow vehicle's brake pedal. Various types of trailer brake systems exist, including vacuum-over-hydraulic brake systems. These vacuum-over-hydraulic brake systems require the generation of a vacuum control signal proportionate to the driver's application of the tow vehicle brakes. In addition to the vacuum control signal, these trailer brake systems require a source of service vacuum to provide the vacuum power needed to operate the trailer's brake system.
Generally, most vehicles with carbureted intake systems generate a sufficient vacuum source at their air intake manifolds to operate not only the tow vehicle's brake system, but also the trailer's brake system, assuming the trailer's size and load to be appropriate for the tow vehicle. However, vehicles with more modern intake systems, such as those equipped with electronic fuel injection, tend to generate insufficient vacuum to operate an independent trailer brake system. These vehicles cannot effectively operate a vacuum-controlled trailer brake system without a supplemental source of vacuum. In the case of diesel engines, practically no vacuum supply is generated, so the entire vacuum supply for a trailer brake system must be generated independently for use with a tow vehicle having a diesel engine.
The requisite vacuum needed to operate a trailer brake system can be supplied by a vacuum pump. Vacuum supplied by a vacuum pump can be used to supplement vacuum supplied by a tow vehicle's engine or serve as the only source of vacuum, depending on the application. The use of both electric and belt driven pumps is known in the art.
Belt-driven vacuum pumps can use rotational motion from the tow vehicle's engine to generate a vacuum supply. These installations require mountings and belts to engage the pump with the tow vehicle's engine. This can be disadvantageous as the pumps, mountings and belts are virtually unique to the particular type of vehicle in which they are installed due to the manufacturer's design of the engine, belt driven accessories, and belt routing. Therefore, because the vacuum pump, its mountings, and belts must be uniquely designed and separately manufactured for each type of vehicle, the belt-driven vacuum pump and its associated mountings and belts are relatively expensive. Additionally, because of the uniqueness of each pump system as applied to a specific vehicle, the pump system cannot be moved from the original truck to a new vehicle of different make and/or model (as used herein, “and/or” means any one, some or all of the things immediately before and after such term).
Electric pumps incorporate their own electric motor that is powered by the tow vehicle's electrical system. Trailer brake systems incorporating electric pumps have the advantage of not requiring elaborate hardware to interface the vacuum pump to the tow vehicle's engine. Because of this, a single design can be used across a number of different types of tow vehicles. Because a vacuum supply can be stored in a reservoir until it is needed for braking operation, it may be desirable to operate the vacuum pump intermittently to extend pump life and/or decrease load on the tow vehicle's engine or electrical system. Desired upper and lower vacuum supply levels can be selected and used to determine whether the vacuum pump should be activated to increase the vacuum supply, or deactivated to conserve the pump life or reduce loads on the tow vehicle's engine or electrical system.
Conditions in which a tow vehicle may operate can vary widely depending on the weather and other atmospheric conditions at a given location. The performance of a vacuum pump system can be affected by these ambient conditions. Specifically, if the vacuum pump system does not account for ambient pressure variation, for example, it is programmed with static vacuum supply levels for turning on and off the pump or it operates for a set period of time after activation regardless of ambient pressure, then the amount of vacuum that can be generated by the vacuum pump will vary with ambient pressure. Therefore, a vacuum pump system operated at a relatively high elevation with correspondingly low ambient pressure, the vacuum pump can be subject to turning on for extended periods of time beyond that necessary to generate a vacuum supply that is adequate to supply sufficient braking power for the trailer brake system. Although this circumstance does not pose a risk from the standpoint of providing adequate braking power, it can result in excessive wear of the vacuum pump. In addition, excessive operation of the vacuum pump may generate unnecessary noise and cause annoyance to the driver of the tow vehicle. It would be desirable to provide a vacuum pump system that ensures an adequate supply of vacuum for trailer brake operation while operating the vacuum pump in an efficient manner.
Therefore, a trailer brake system is needed that can compensate for the effects of ambient conditions on vacuum pump performance.